I think they are different beasts really. The M401/Evo is very small, but punches above its weight. Its main downside, IMO, is fiddly cartridges. They are not that easy to top up. Do it carelessly and you will get a mouthfull of e-liquid. The 901 cartridges are much easier in this respect. However, it gives a better "smoking" experience than any 901 I've tried IMHO..
I've not tried the Joyetech/Dura. It looks like when it works it should be good. It seems like a 901 on steroids, which appeals to me. I'm still doubtful about spending so much on an item which seems to have a fairly high chance of being defective. Battery problems seem to be common, judging by what's being posted here. If they ironed out the issues, and reasonably priced spare parts were available, then I'd be tempted.
Neither is perfect.